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Friday, March 15, 2013

This is an excerpt from Philosophy of Religion by C. Stephen Evans in the chapter for classical arguments for God's Existence. In this excerpt, Evans describes Norman Malcolm's formulation of Anselm's second ontological argument, which deals with the concept of necessary existence.The gist of the second argument, as Malcolm formulates it, is as follows: God is by definition a being who does not merely happen to exist. God can neither come into existence nor pass out of existence, since a being who could do either simply would not be God. It follows from this that if God exists at all, then his existence is necessary. If he does not exist, then his existence is impossible. But either God exists or he does not exist, so God's existence is either necessary or impossible. Since it does not seem plausible to say that God's existence is impossible, then it follows that his existence is necessary. So if God's existence is possible, then it is necessary. More formally the argument can be put like this:

1. If God exists, his existence is necessary.
2. If God does not exist, his existence is impossible.
3. Either God exists or he does not exist.
4. God's existence is either necessary or impossible.
5. God's existence is possible (it is not impossible).
6. Therefore God's existence is necessary.1

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comments
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1) It is possible that a maximally great being exists2) If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.3) If a maximally great being exists in some possible world, then it exists in every possible world.4) If a maximally great being exists in every possible world, then it exists in the actual world.5) If a maximally great being exists in the actual world, then a maximally great being exists.6) Therefore, a maximally great being exists.

bmzimmerman's response is fairly damning, I'd say, although I would add that there's a further problem of multiple uses of "possible" and "impossible." The first "impossible" is used to mean that if God did not exist already, He could not come to exist. So, "possible" used as the opposite of that specific "impossible" would mean able to come into existence. God's existence is not "possible" in that narrow sense; it is possible in the different sense that He may have existed for all time. That's the original "if" clause. So, there's a kind of subtle semantic switch that happens between #2 and #5.

1. If Zeus exists, his existence is necessary. [non-sequitur]2. If Zeus does not exist, his existence is impossible. [non-sequitur]3. Either Zeus exists or he does not exist. [valid]4. Zeus’ existence is either necessary or impossible. [Major premise, non-sequitur]5. Zeus’ existence is possible (it is not impossible). [Minor premise]6. Therefore Zeus’ existence is necessary. [Conclusion, invalid and circular]